The plasticity of the nervous system and the neural mechanisms for gating of sensory information are two of the general topics with which this application is concerned. The experiments described will attempt to resolve the question of whether observed changes in neuroelectric activity during conditioning are indeed the neural correlates of learning or are epiphenomena which can be accounted for by some other variables. In a previous study we have found that potentials evoked by a background stimulus during conditioning show changes similar to those which have been reported to occur with conditional stimuli. In these experiments both relevant and irrelevant stimuli will be presented simultaneously. If the changes in brain electrical activity evoked by both relevant and irrelevant stimuli are similar, then the implication would be that hitherto reported correlations between learning and evoked potential shapes are epiphenomena. If they show a difference, then we will attempt to explore further the nature of this difference and the brain structures which help mediate the discrimination between relevant and irrelevant information. The difference, if any, between the CS and background evoked potentials might indicate that at least part of the changes in evoked potentials are due to a process associated with learning or memory. The design of these experiments will enable us to further investigate the neural mechanisms for selective attention. We hope the results of these studies will further our understanding of the underlying causes of "learning disabilities" in children.